When too many terminals, for example, stations (STAs) are present in a wireless local area network (WLAN), a probability that the STAs collide with each other increases. When an STA that performs channel access without listening to a beacon or an STA of an overlapping basic service set (BSS) or neighboring BSS conducts channel access, the STAs may compete with an STA allocated a slot through a beacon.
Thus, the STA performs channel access in a distributed coordination function (DCF) mode even in the allocated slot. However, when there are relatively more STAs the which slots are not allocated than STAs to which slots are allocated in the DCF, a great number of STAs perform channel access for a short period of time, thus increasing a delay in channel access.
For example, when an STA corresponding to a bit set to “1” in a traffic indication map (TIM) performs channel access to receive buffered data, a delay may occur. Further, in the presence of a hidden node in an uplink, a collision probability increases.
Also, it is important for a terminal or sensor considering power saving to reduce time to detect a channel by decreasing collisions.
A slot size is determined in advance before a beacon is transmitted. Here, an STA may transmit all data using only a portion of a slot. When another STA uses a remaining period of the slot or unused slot period, network resources may be efficiently used.